Londoners find cracks in their homes after successive heat waves

(Bloomberg) --Londoners are facing historic levels of subsidence risk after five successive heat waves dried out the clay soil on which much of the city is built.

Insurance claims tied to subsidence — a phenomenon associated with bouts of hot, dry weather that shrink the soil and destabilize the foundations on which buildings stand — hit a record last quarter, according to data provided by the Association of British Insurers. On average, households claimed £20,000 ($27,200) for the risk, more than in any previous quarter and a 15% jump from the same period in 2025, the ABI said.

Laura Hughes, head of general insurance at the ABI, says the upward trend is likely to continue. "We expect to see more subsidence cases because of the hot weather," she said in an interview. 

Londoners have taken to social media to express their dismay. On Reddit, people offered personal accounts telling of "horrendous cracking" in their homes, and "doors sticking" due to subsidence. One said it was "genuinely scary" to discover that their kitchen had moved as the foundations of the home shifted.

Another Reddit user described the response of a structural engineer they contacted for help. "Before I could finish explaining he laughed and said, 'You and 20,000 other people in southeast London'," the person wrote.

"It's crazy, what's happening now," said Otso Lahtinen, chief executive of Geobear, an engineering firm that's regularly called in to repair damage caused by subsidence. "It's the new norm, and it seems it will happen more often in the next 20-30 years."

Data provided by Aviva Plc show that the areas of London that are most at risk are some of the UK capital's most sought after, namely the boroughs of Westminster, as well as Kensington and Chelsea. While subsidence has been affecting homes in the British capital for decades, climate change is making it worse. London clay is especially sensitive to fluctuations in moisture, expanding when wet and contracting when dry. 

The threat of subsidence in the UK is concentrated in and around London as well as in parts of the southeast. In the four years through 2025, insurance payouts for subsidence damage soared roughly 90% to reach a record £297 million, according to data provided by the ABI.

The most vulnerable properties are Victorian or Edwardian homes that were built directly onto the upper layers of London clay. By contrast, modern office buildings in the City of London and Canary Wharf have much deeper foundations and are therefore less exposed to such risks. 

Subsidence is part of a long list of heat-related challenges to which the UK is now struggling to adapt. Over the past months, extreme heat has forced schools to close, led bus drivers to go on strike, and seen banks relax in-office work requirements to protect staff from unbearably hot commutes. Most of England has been gripped by drought and the country's hospitals have shown signs of buckling under the strain.

London Mayor Sadiq Khan has warned that the city will need to turn to private investors to help fund the cost of dealing with the impact of rising temperatures. His office estimates that London now faces an annual bill as high as £36 billion into the 2050s in order to prepare the city for what climate change has in store.

"The impact that climate change is having is undeniable," said Hughes of the ABI.

Subsidence can devalue a property by an average of 20%-25%, according to the Federation of Master Builders. In some cases, homeowners prefer to cover the cost themselves rather than wade through complicated claims processes. The traditional engineering fix for subsidence damage, known as underpinning, can cost anywhere from £20,000 to more than £100,000. 

The development represents a particular risk to insurers, with subsidence claims making up an ever larger chunk of the payouts they need to make to customers. 

The phenomenon poses "a significant challenge for UK home insurers," says Cherry Chan, a partner at Deloitte. The consultancy has warned that UK home insurers risk losses in 2026 due in part to the trend.

Along with flash floods and wildfires, subsidence is becoming "an increasingly material climate-related risk," Chan said. It requires that insurers display "careful consideration in long-term exposure and risk management strategies." 

Extreme weather patterns in 2026 "will not only impact more new claims in this year, but could cause claims deteriorations for unsettled subsidence claims reported in the past," she added. That includes 2025, which was a so-called surge year for subsidence impacts.

Fresh estimates from the British Geological Survey indicate that under what is known as the RCP 4.5 emissions scenario — reflecting a trajectory that closely aligns with current climate policies — 1.8 million properties, or about 5% of the UK total, are "highly likely or extremely likely" to be susceptible to shrink-swell subsidence by 2070. Under a higher emissions scenario, the figure rises to 4.2 million, or 11%, of British properties. Areas most at risk are densely-populated parts of London, Kent and south-east of England.

The development has the potential to lead to "increased insurance premiums, depressed house prices and, in some cases, engineering works to stabilize land or property, replacement of utility pipeworks and unstable transport infrastructure," according to the BGS.

Geobear, which tackles subsidence by injecting resin under buildings, says it's received more homeowner inquiries this summer than ever before. It says insurance clients have confirmed a similar trend, with one telling Geobear it had received 180 claims on a single day, which is significantly more than normal.

"It's a pretty severe situation," said Lahtinen, the CEO. "If you're looking to trade, sell or buy property, this is a trend you can't ignore."